High-frequency duplex signaling system



Dec. 25, 1928. 1,696,595

E. F. CARTER HIGH FREQUENCY DUPLEX SIGNALING SYSTEM Filed Jan. 27, 1925 VWW AJI

Inventor Emmett, F- Carter:

His Abnorneg- Patented Dec. 85,1988,

UNITED STATES PATENT OFFICE.

EMMET-I' I. CARTER, OI SCHENECTADY, NEW YORK, ASSIGhTOB TO GENERAL ELECTRIC COMPANY, A CQRPORATION OF NEW YORK.

men-answerer nu'rnnx sreimnms sYsrnrL Application filed Ianuar m, 1925. Serial m. 5,148."

My present invention relates to signaling systems adapted to duplex operation, and more particularly to high frequency signaling systems of the carrier current type.

c- 011s of the objects of my invention is to provide a system whereby duplex operation may be carried on by the use of a single high frequency for the carrier currents transmitted in both directions.

vide a transmitting apparatus which wi be operative only when a signaling potential is impressed thereon.

Still another object of my invention is to provide means whereby both a transmitting apparatus and a sensitive receiving apparatus may be simultaneously coupled to a signaling circuit without injury to the receiving apparatus when the transmitting apparatus is in operation.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its to organization and method of operation, will best be understood by reference to the following description taken in connection with the accompanying drawin on which I have shown diagrammatically one circuit organization which may be used in carrying my invention into efiect.

l have indicated in the drawing the appli cation of my invention to a duplex carrier c ent telephone system. for communicaover a circuit which is merely indicated he conductor l. The circuit may be an r communication circuit, or a power say be a radio transmitting circuit. .nsmitting apparatus comprises a ctrode electron discharge tube 2, -ich serves as a generator of oscillations,

an amplifying tube 8 which serves to amplilty the oscillations produced by tube 2, a mod ulatin tube 4- serves to modulate the amplified oscillations of tube 3, an amplit'ying tube 5 for amplifying speech currents produced by telephone transformer 6 and supplying the amplified speech currents to the input or control circuit of modulator 4, and control tubes 1 and 8 for controlling the operation of oscillator 2.

The cathodes of all of the tubes mentioned are connected in parallel and supplied with heating current from an alternating current source 9 through a transformer 10. Plate Anotherobject of my invention is to 1'0 plate circuit of control tube 7 includes the resistance 17, which is also included in the grid circuit of oscillator 2. The plate circuit of tube 8 includes a resistance 18, a portion of vvlgicl; is connected in the grid circuit of 'lhe grids of modulator tube ei'and control tube 8 are connected together and are normally biased negatively by the source 19. When no signaling current is impressed upon the system the voltage of the source 19 is so chosen that substantially no current will flow in the plate circuit of tube 8. As a result the grid of tube 7 will be of substantially cathode potential and current will flow in the plate circuit of tube 7 of such a value as to reduce a voltage drop through resistance l of such value as to provide a negative bias on the grid of oscillator 2 high enough to prevent the production oi oscillations.

l? hen speech currents are produced by microphone 6 the output of amplifying tube 5 is supplied through transformer 20 to the grids of tubes 4 and 8. As a result, the grid of tube 8 will become suficiently positive to permit current to flow in its plate circuit. This will result in the production of a nega tive bias on the grid of tube 7, which will cut down the current in its plate circuit, and also reduce the negative bias on the oscillator grid suficiently to permit. the production of oscillations. The oscillations produced will be modulated by the action of tube 4 in a well known manner.

While the plate circuits of tubes 7 and 8 are supplied with alternating potential, the condensers 21 22 have suflicient storage capacity to prevent the voltages applied to the grids of tubes 2 and 7 falling at any time below the cutod value. By means of these condensers the potential on the grid of the device 2 is smoothed suficiently to prevent any substantial modulation of the currents loll lOh

produced by the oscillator in accordance operation of the system described is substantially instantaneous, particularly if alternating current source 9 is of a frequency about equal to the normal voice frequency and that transmission starts at almost the same instant that a signaling current starts in the microphone.

For reception the receiving circuit may be coupled to the transmitting circuit through a coupling transformer 23, the secondary of which'is included in a tuned link circuit 24.

This link circuit, in turn, is coupled to a tuned circuit 25, which may be connected to any desired form ofreceiver. To protect the receiving apparatus from the effect of potentials which may be impressed thereon by the transmitting apparatus when the latter is in operation, I provide in shunt to the link circuit 24., a path which oifers a substantially infinite impedance to thereceived currents, but a comparatively low impedance to currents impressed upon the link circuit 18 from the transmitting apparatus. This device as indicated in the drawing consists of an electron discharge tube 26 having its grid and anode connected together and made slightly negative by battery 27. When signaling currents are being received the impedance of tube 26 is practically infinite; hence, the operation of the receiving system is not interfered with in any way. When, on the other hand, the transmitter is operating and a high voltage is impressed upon the link circuit 24; the anode of tube 26 will become positive, consequently, its impedance will be greatly reduced. As a result, a large portion of the energy impressed upon the link circuit will be shunted through tube 26, thus partially detuning the link circuit and increasing its impedance, thereby greatly reducing the potential impressed upon the receiving apparatus. By this expedient I have found that the receiving apparatus will be effectively protected from injury and that it will always be in condition to receive and indicate received signals as soon as the transmitting apparatus has ceased operation.

While I have shown and described the apparatus required for one end of a duplex signaling circuit, it'will, of course, be understood that the apparatus at the opposite end may be an exact duplicate of that shown and described. It will also be apparent that the system shown and described will be adapted to any form of high frequency signaling desired, either over wire lines or radio, and for telegraphic signaling, as well as telephonic.

What I claim as new and desire to secure by Letters Patent of the United States, is,- 1. In a transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a control device for said oscillator comprising means for normally providing a ne ative bias on the grid of said oscillator sufficient to prevent the production of oscillations and means responsive to an audio frequency signaling current for reducing the negative bias to a value at which oscillations will be produced, the bias potential being sufiiciently smoothed substantially to prevent modulation by voice currents of the oscillations produced.

2. In a transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a control device for said oscillator comprising means comprising a second electron discharge device for normally providing a negative bias on the grid of said oscillator sufiicient to prevent the production of oscillations and means responsive to signaling current for controlling the current through said second device and thereby reducing the negative bias of the oscillator grid to a value at which oscillations will be produced, the bias potential being sufficiently smoothed substantially to prevent modulation by voice currents of the oscillations produced.

3. A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a second electron discharge device having included in its plate circuit a resistance which is included in the grid circuit of the oscillator, said second device being normally so adjusted that the current flowing in its plate circuit will produce a negative bias on the grid of the oscillator sufficient to prevent the production of oscillations and means responsive to. signaling current for controlling the current through said second device and thereby reducing the negative bias of the oscillator grid to' a value at which oscillations will be produced, the bias potential being sufficiently smoothed substantially to prevent modulation by voice currents of the oscillations produced.

4". A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, means comprising a second electron discharge device for normally providing a negative bias on the grid of the oscillator sufiicient to prevent the production of oscillations and a third electron discharge device for controlling the current through the second device and thereby reducing the negative bias of the oscillator grid to a value at which oscillations will be produced, said third device being controlled in its action by the signaling current to be transmitted.

5. A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a second electron discharge device having included in its plate circuit a resistance which is included in the grid circuit of the oscillator, said second device being normally so adjusted that the current flowing in its plate circuit will produce a negative bias on the grid of the oscillator sufficient to prevent the production of oscillations, and a third electron discharge device for controlling the current through the second device and thereby reducing the negative bias of the oscillator grid to a value at which oscillations will be produced, said third device being controlled in its action by the signaling current to be transmitted.

6. A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a second electron discharge device having included in its late circuit a resistance which is included in the grid circuit of the'oscillator, said second device being normally so adjusted that the current flowing in its plate circuit will produce a negative bias on the grid of the oscillator sufficient to prevent the production of oscillations, and a third electron dis charge device having included in its plate circuit a resistance which is also included in the grid circuit of the second device, said third device being controlled by the signaling current to be transmitted in such a way that application of the signaling current thereto will cause the negative bias of the oscillator grid to be reduced to a value at which oscillations will be produced.

7. A transmitting apparatus for a high frequency signaling system comprising an electron discharge oscillator, a second electron discharge device havin included in its plate circuita resistance w ich is included in the grid circuit of the oscillator, said sec-- ond device being normally so adjusted that the current fiowin in its plate circuit will produce a negative ias on the grid of the oscillator suflicient prevent the production of oscillations, and a third electron discharge device having included in its plate circuit a resistance which is also included in the grid circuit of the second device, said third device having its grid normally biased to a negative value suflicient to substantially prevent the flow of current in its plate circuit and being controlled by the signaling corrent to be transmitted in such a way that the application of a signaling current thereto'will cause the negative bias of the oscillator grid to be reduced to a value at which oscillations will be produced.

8. A transmitting apparatus for a high frequency signaling system comprising 'an electron discharge oscillator, a second electron discharge device having included in its plate circuit a resistance which is included in the grid circuit of the oscillator, said second device being normally so adjusted that the current flowing in its plate circuit will produce a negative bias on the grid of the oscillator sufiicient to prevent the production of oscillations, and a third electron discharge device having included in its plate circuit a resistance which is also included in the grid circuit of the second device, said third device having its grid normally biasedto a negative value sufiicient to substantially prevent the flow of current in its plate circuit and being controlled b the signaling current to be transmitted 1n such a way that application of the signaling current thereto Wlll cause a negative bias to be produced on the grid of the second device.

In witness whereof, I have hereunto set my hand this 26th day of January, 1925.

EMMETT F. CARTER. 

